linux-kernel - Re: CVE-2025-40128: btrfs: fix symbolic link reading when bs

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Message-ID: <20251113104008.GM13846@twin.jikos.cz>
Date: Thu, 13 Nov 2025 11:40:08 +0100
From: David Sterba <dsterba@...e.cz>
To: cve@...nel.org, linux-kernel@...r.kernel.org
Cc: linux-cve-announce@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...nel.org>
Subject: Re: CVE-2025-40128: btrfs: fix symbolic link reading when bs > ps

On Wed, Nov 12, 2025 at 07:24:04PM +0900, Greg Kroah-Hartman wrote:
> From: Greg Kroah-Hartman <gregkh@...nel.org>
> 
> Description
> ===========
> 
> In the Linux kernel, the following vulnerability has been resolved:
> 
> btrfs: fix symbolic link reading when bs > ps
> 
> [BUG DURING BS > PS TEST]
> When running the following script on a btrfs whose block size is larger
> than page size, e.g. 8K block size and 4K page size, it will trigger a
> kernel BUG:
> 
>   # mkfs.btrfs -s 8k $dev
>   # mount $dev $mnt
>   # mkdir $mnt/dir
>   # ln -s dir $mnt/link
>   # ls $mnt/link

Please drop the CVE status from this patch, the bs > ps (block size
bigger than page size) feature requires CONFIG_BTRFS_EXPERIMENTAL and is
unfinished and possibly unstable in other use cases. It does not make
sense to improve security where none should be expected.